The high temperature process for producing 1,2-dichloroethane by a liquid phase reaction of ethylene with chlorine at a temperature of 65.degree. to 160.degree. C. in the presence of a metal chloride catalyst in a reaction medium containing 1,2-dichloroethane as a main component has been known in U.S. Pat. No. 2,929,852, U.S. Pat. No. 3,839,475 and British Pat. No. 1,422,303. In accordance with such high temperature process, 1,2-dichloroethane as the reaction product can be obtained in a form of vapor. In such process, the reaction zone can be effectively cooled by the latent heat resulted in the evaporation of 1,2-dichloroethane, whereby a special means for cooling the reaction zone can be advantageously eliminated. Moreover, a heat source for rectification of the product can be saved by feeding the vaporized 1,2-dichloroethane into a rectification tower for purification of 1,2-dichloroethane as a vapor. Both effects are attained.
Recently, such high temperature process has been considered to be important in view of energy saving. Such high temperature process has said advantages, however, has a fundamental disadvantage that the side reaction for producing 1,1,2-trichloroethane is significant at a reaction temperature of 60.degree. C. or higher especially higher than a boiling point of 1,2-dichloroethane as the reaction medium (83.degree. C.) to be lower selectivity to 1,2-dichloroethane as the object product and to be lower yield. Heretofore, a process for overcoming such disadvantages in the high temperature process has been also proposed. For example, British Pat. No. 1,186,742 discloses a process for reducing a production of 1,1,2-trichloroethane by adding only a small amount of oxygen to the reaction mixture by using oxygen as a side reaction inhibitor. The process, imparts the effect for reducing the production of the by-product, however, it has a disadvantage that the unreacted ethylene and oxygen are remained in an uncondensed gas separated from a condensed liquid in a condensation and liquefaction of the resulting 1,2-dichloroethane distilled from a tower top and an explosive mixture is formed by the unreacted ethylene and oxygen.
It is necessary to consider a treatment for preventing the trouble.
In U.S. Pat. No. 3,911,036, a two step reaction process is employed. The first step, imparts a conversion of about 17%, at high temperature and the second step imparts a remained conversion at low temperature to reduce the production of the by-product. The two step reaction process has a fatal disadvantage of causing a complication of the process.